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Figs. 3 and 4 show sections of the rail now in use on the State Street cable line, the height of the head being 1 inches. The first rail put in on State Street, Chicago, had a head 34 inch high. This was increased to 1 inch and later to 136 inches. It is beveled to conform with the bevel of the car wheel for two-thirds of its section from guage line across the head.
Many will ask, no doubt, if there is not a slipping of the wheels on the rails, due to the unequal diameter of the wheel at all points ? There is, if we imagine the wheel divided into three parts at rightangles to its axis (Fig. 3), and each piece free to move by itself, and whose diameters are situated at a, b, and c, respectively; and it is quite evident that as the portion (a) makes one revolution it will travel over a less distance than the portion (6) would, and similarly the portion (c) will travel farther than the portion (6) in one revolution, but on account of it being all one, the portion (a) travels farther than it otherwise would, thereby causing it to slip; the portion (c) would travel a less distance than it otherwise would, thereby causing it also to slip.
The above is based on the supposition that the car would move a distance equal to the circumference of the wheel at the point (6) in one revolution of the wheel. But this waste of power due to slipping is very slight, for, considering the co-efficient of friction as .15, we find that for a ton mile the energy lost by this slipping is .0104 H. P.; so small, in fact, that, on account of other advantages, it may be ignored.
The experience of the Chicago City Railway Company, which first tried this form of head, has been that it saved wear of both rails and wheels, increasing their life by about thirty-five per cent. Why not, in building a track, put in rails which are beveled to conform to the shape of the car wheel at the first, and not spend time and money wearing the wheel and rail down to fit each other ?
Fig. 5 shows a section of a new and old car wheel which illustrates clearly the manner in which the tread of the wheel will wear if used on a rail with no bevel. The record of car mileage of this wheel is not known, but no doubt a great amount of energy was lost before it had worn down to its most economical state.
Fig. 6 shows a rail taken from the State Street track after eight years' wear, during which time 8,000,000) car wheels passed over it.
Fig. 7. Fig. 7 shows a rail when taken out after eleven vears' wear. The rail should have been taken out three years previous, but owing to impossibility of getting rails at the time, and the World's Fair occurring at that time, the track was not rebuilt. The true rate of wear cannot be found, as the flange of the wheel had begun to run on the flange of the rail long before it was taken out. The dotted lines show an interesting state of affairs. This section shows the wear due almost entirely to wagon traffic.
Fig. 8 shows the rail used at the present time in our 7 inch construction with chairs or tie plates. The rail weighs 83 pounds and has a head 13 inches high, beveled as described.